This application claims the priority of German Patent Application Serial No. 297 21 760.7, filed Dec. 10, 1997, the subject matter of which is incorporated herein by reference.
The present invention relates to a non-detachable, cold-formed press fit arrangement between an end portion of a metal pipe in a socket of a fitting, with the socket formed with an annular anchoring groove facing interiorly of the socket for receiving a sealing ring.
In general, a press fit arrangement between the socket of a fitting and an end portion of a metal pipe up to an inside diameter of 54 mm is realized by an electrohydraulic press tool which is provided with a crimping bracket having two jaws that bound a compression zone. These jaws are swingably mounted to adapters which extend transversely to the longitudinal axis of the bracket. The jaws grab around the socket of the fitting in the area of a bead for receiving the sealing ring and on both sides of the bead. A force is applied immediately before, on and behind the bead to realize a non-detachable joint. Through cold formation of the bead, the sealing ring is pressed onto the pipe end while indentations spaced about the circumference are formed before and behind the bead for plastically deforming the pipe end in the area of the indentations.
When greater diameters of metal pipes are involved, the use of a crimping bracket whose jaws are directly placed over a fitting is inadequate to effect a cold forming operation of the fitting and the inserted end portion of the metal pipe. In order to non-detachably bond pipes with an inside diameter of 70, 80 or 100 mm through cold forming, the use of electrohydraulically operated tools is known which are however bulky and difficult to handle. These tools are provided with a wraparound ring which is placed over the socket of a fitting after inserting the end portion of the metal pipe in the socket. By means of the wraparound ring, the inwardly open bead, which receives the sealing ring, and the area of the socket neighboring the bead together with the pipe portion located in this area are commonly deformed in a triangular shaped manner, whereby the sides of the triangle assume a curved configuration and the corners are rounded.
It is also known to provide the fitting with smooth ends and to produce the bond between one end of the fitting and an end portion of the metal pipe by utilizing a socket in which the end of the fitting and the end portion of the metal pipe are inserted, and which is slotted in longitudinal direction. The width of the slot can be decreased by means of locking screws so that the socket is pressed onto the ends of the fitting and the metal pipe. A seal is placed in the socket for circumscribing the ends of the fitting and the metal pipe.
It is an object of the present invention to provide an improved press fit arrangement between a fitting and a metal pipe, obviating the afore-stated drawbacks.
In particular, it is an object of the present invention to provide an improved press fit arrangement for use with metal pipes of an inside diameter exceeding 54 mm, which realizes a round or substantially round cross-section of the socket even in the crimped end state whereby the sealing forces and holding forces about the entire circumference are the same or substantially the same.
These objects, and others which will become apparent hereinafter, are attained in accordance with the present invention by providing a socket which is formed with an annular anchoring groove facing inwardly for receiving a sealing ring, and by securing at least one holding element to the socket and cold forming the holding element together with the socket, with the holding element at least partially penetrating the material of the end portion of the metal pipe to realize a positive fit with the metal pipe.
According to one embodiment of the invention, the socket is formed adjacent the anchoring groove for the sealing ring with an annular receiving groove facing the interior space for receiving the holding element, whereby the holding element is provided with projections spaced about the circumference of the holding element and pointing towards the end portion of the metal pipe, or with a circumferential cutting edge extending towards the end portion of the metal pipe. When cold forming the socket of the fitting, the projections or the cutting edge realize the positive fit between the holding element and the end portion of the metal pipe.
The holding element may be a ring formed with an axial slot, with the ring-shaped holding element having a cross section in the form of a vertex of a triangle (or pointed roof configuration), or a curved cross section or a polygonal cross section. It is also possible to configure the receiving groove with a conical base, whereby the holding element has a cross sectional contour which complements the conical base of the receiving groove and includes a free edge of small diameter for penetration into the end portion of the metal pipe after radially compressing the socket.
According to another feature of the present invention, the socket of the fitting may also be provided adjacent the entry opening for the metal pipe with an outwardly directed annular anchoring groove for accommodating an anchoring flange of a sleeve-like holding element.
According to still another feature of the present invention, the anchoring groove is formed in a bead of the socket, with the holding element being a stepped sleeve having a first portion of smaller diameter and a second portion of greater diameter, with the second portion overlapping the bead of the socket, and with the first portion surrounding the metal pipe. After crimping operation, the holding element matches the outer contour of the socket, with the first portion of the stepped sleeve denting the material of the metal pipe.
Suitably, the socket of the fitting has an outer peripheral surface provided with an engagement member in form of a circumferential groove, lobes, ribs or circumferential fins for attachment of a press tool, preferably a wraparound chain.
According to yet another feature of the present invention, the holding element has a hardness exceeding a hardness of the metal pipe. Preferably, the holding element is made of special steel.
A press fit arrangement in accordance with the present invention realizes a positive fit between the holding element, which is secured to the socket of the fitting, and the metal pipe by providing the holding element with spikes, teeth, crawls or cutting edges which dig into the material of the end portion of the metal pipe during crimping operation. It is also possible to provide the holding element in the form of an axially slotted sleeve which surrounds the metal pipe and partially dents the material of the metal pipe.